Electric power systems generally include high voltage (>69KV) transmission lines from a generating means, a number of substations, and a network of distribution (<69KV) and feeder lines for the delivery of electric power to the customers. An electric power system typically includes a number of protective relays, as well as other protection devices, which monitor the operation of the power system and determine, among other things, when and where a fault occurs in the system. Circuit breaker devices are in turn controlled by the protective relays.
Historically, protective relays were mechanical or electro-mechanical (a large number of such relays are still in use), while more recently, protective relays are typically microprocessor-based and are usually referred to as digital or computer relays. These computer relays typically record a significant amount of information for the power lines associated with the substation, including voltages and currents on the power lines, as well as complete “event” information relative to any abnormal (fault) conditions. This information is stored in the memories of the computer relays.
The relays provide output signals, when appropriate, which are used to control associated circuit breakers operating on the power lines. The information stored in such relays can be transmitted to a central facility and/or accessed locally via a printer terminal. Comprehensive system monitoring is accomplished by what is known generally as a SCADA system, which stands for Supervisory Control and Data Acquisition, and which is widely known and used.
A development which resulted in some communication integration of the various protective relays and other supporting devices at a substation is known as a protective remote terminal unit (PRTU). The PRTU includes a modem for remote telephone communication, as well as control software for basic communication purposes, and is capable of handling input information from several different protective relays. The PRTU includes a simple data buffering capability, as well as a local port for a terminal, printer or computer. Another development, known as a display transducer adaptor (DTA), provides analog output information from the digital information available from microprocessor-based protective relays. This is helpful for integration of the protective system with analog SCADA remote terminal units. Such a system is shown in U.S. Pat. No. 5,160,926, which is assigned to the same assignee as the present invention.
In another system integration approach, each protective relay or other intelligent electronic device (IED) in the protection system is connected to a communication network bus through a network interface module (NIM). Each NIM must be separately programmed to retrieve, store and distribute IED information. A human machine interface, such as a personal computer with a monitor, provides local control and monitoring. The system can communicate with a SCADA system through a remote terminal unit at the substation. A modem may also be included, for communication with remote network devices.
Some of the prior communication integration systems included the capability of automatic scanning port-to-port for any data present at the port data buffers. Some systems could also respond directly to a particular port upon an indication of a fault condition recognized by the relay connected to that port. Some terminal units had additional data buffering capability, enabling them to communicated with a central monitoring (SCADA) system or a computer system through a conventional modem. In some systems, the data had to be reformatted to an ASCII format for use by a printer. Other devices, however, were completely transparent to the data received from their ports.
The systems described above, while achieving some communication integration at the substation level, were not capable of processing the information received from the ports, nor did those systems have a database capability. These disadvantages significantly limited the capability of the communications systems. It was the applicants herein who recognized the full communication integration opportunities possible at the substation level and developed an apparatus to take advantage of those opportunities.